Previous research in our group has focused primarily on the d8 metals Pd(II) and Pt(II) with the thiacrown macrocycle 9[ane]S3 (1,4,7-trithiacyclononane). Recently, we have explored fundamental aspects of 9[ane]S3 Au(III) chemistry. We chose to explore Au(III) complexes because they should exhibit square planar geometry, but Au(III) has significantly different redox properties. Numerous unexpected reaction products of Au(III) and 9[ane]S3 were obtained, many of which could only be first identified by X-ray crystallography.  These structural results then allowed us to determine a reasonable synthetic route to reproduce these products.  The 9[ane]S3 ligand was especially remarkable because subsequent reactions of Au(III) coordinated to a 9[ane]S3 ligand yielded unusual C-H bond activation of the 9[ane]S3 ligand at low temperature (50o C).  The product of this activation was a chiral sulfonium cation.  We have isolated [AuCl4]- and [AuCl2]- salts of the bicyclic chiral sulfonium.  The chiral sulfonium salts were characterized by 1H, 13C,and DEPT NMR experiments, X-ray crystallography, and elemental analysis. Similar sulfonium salts with a different anion have been reported; however the role of Au(III) in their synthesis was unclear.  Since we were able to develop a rational synthesis of the chiral sulfonium salts utilizing Au(III),  we have now gone on to monitor and quantify the reaction rate to produce the sulfonium derived from 9[ane]S3.  The mechanistic details of these Au(III) coordination reactions with regards to C-H activation are currently being pursued.

C-H activation at gold(III): Synthesis of chiral sulfonium salts

247th National Meeting (2014)

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